Significant advances in commercially available vertical cavity surface emitting lasers (VCSELs) have been made due to the introduction of oxide apertures.
An oxide aperture may be formed by an oxidation process in which an AlGaAs material is transformed into an AlOx:As form as a result of chemical reaction of H2O molecules with the AlGaAs material while an AlGaAs layer is exposed to a high-temperature N2 and H2O mixed gas atmosphere and the H2O molecules are diffused inside the AlGaAs layer.
Since such a chemical oxidation process is highly dependent on processing conditions such as an Al content of an AlGaAs layer, a content of water vapor, a temperature of a reaction chamber, and the like, it is difficult to precisely control shapes and sizes of oxide apertures in a lateral direction. Therefore, there is a problem in that it is difficult to uniformly form oxide apertures on the same wafer.
Currently, formation of oxide apertures is precisely controlled using an expensive commercial manufacturing process apparatus. However, fundamental problems are not solved yet, and only production costs are increased. In addition, there is a problem in that an error of 1 μm or more occurs even when such a precise apparatus is used. [See M. Grabherr, D. Wiedenmann, R. Jaeger, and R. King, “Fabrication and performance of tunable single-mode VCSELs emitting in the 750 to 1,000 nm range,” Proc. SPIE 5737, 120-128 (2005)]. Generally, since a diameter of an oxide aperture of a VCSEL device ranges from about 3 to 10 μm, a process error of 1 μm may significantly degrade a yield of the device.
Further, work efficiency may be extremely lowered because an oxidation process should be performed on wafers one by one for precise control.